Possible bad O2 sensor?

[crazyvwvanman]

Voltage drop only occurs when CURRENT is flowing.
It means nothing if you measure for alternator charging voltage drop without the alternator spinning and providing significant amps through the path you are measuring.
Same in the other direction.
You must have significant current flow from the battery through the path you are checking to check for voltage drop.

Mark

[AirCooledCurtis]

[do.dah]

[AirCooledCurtis]

[AirCooledCurtis]

Another update, the battery was not the problem. I'm not sure why it worked for a moment it seemed. Today I pulled it out to do a test drive and it was doing the same thing. Disconnect o2, do a key cycle, and it will drive. It doesn't run well under load below 2500rpms or so with the o2 unplugged, but I'm not going think about that right now. I tested the o2 volts at the circuit board on the ECU while idling, and it's the same as at the connector in the engine bay. I'll reiterate, it idles incredible. It revs freely right after a key cycle. It will completely die with any throttle at all after 15 seconds to a minute of idling. The replacement ECU will be here sometime today.

[AirCooledCurtis]

The ECU I got in the mail from eBay is 1: DOA, 2: a 022 stuffed inside a 022D case, and 3: someone "attempted" to repair it and just really messed up the PCB. So now I have to wait another week until one gets here. Also the IAC hasn't been working, so I got to that in the mean time and transistor is fried in the idle control module as usual so I've got to repair that. It idled well though. IAC is closed, clamping the IAC hose doesn't change anything. The airflow bypass screw in the throttle body is 2 turns from the bottom. Maybe someone forced the throttle plate to stay open a little? I'll have to pull that off next, since I know that the 2.1 WBX throttle closes completely, with that little notch for the screw, but that's nowhere near enough air volume for this engine to run. The AFM is generating the correct output at idle, so it's got to be a hole in the throttle body. From my experience with Digifant, usually with no idle air module it'll just die when you aren't physically holding the throttle open.

Edit: I just pulled the throttle body, and it's fine. It's still strange to me that it idles fine with the throttle closed, and IAC dead/unplugged/hose clamped etc.

[jlrftype7]

[AirCooledCurtis]

[AirCooledCurtis]

Another 022D arrived, this one a silver label from 1998. Same thing as before, though a key cycle doesn't seem to cure the issue the same as before. When warm does the later ECU enter closed loop sooner than the 022? I'm running out of ideas. My reasoning why it can't be the AFM is that 1: it will rev okay on a cold start, and 2: I physically tested output voltage, and had the cover off when running. Forcing the engine into open loop cures the issue but it doesn't run incredible. I'll do a deep dive into the CTS "temp 2". I've heard that unplugging it will force an open loop. A bad CTS causing a rich condition at temp is common, I haven't seen a bad CTS cause a lean condition so bad the throttle switch turns into an engine off switch. (BTW still a fantastic idle, no issues there). Another thing I've considered is even though the O2 is brand new from Bus Depot (not the solder yourself kit) and it swings from .1V to 1V at idle it could be bad, somehow. I verified no exhaust leaks, again.

[AirCooledCurtis]

I'm thinking I've found the problem, with the O2 signal wire unplugged, ECU unplugged, the pin 19 reference ground unbolted from the head, I get anywhere from 4 to 220k ohms from the pin 19 wire terminal to the chassis. So looking at the wiring diagrams, there's a short somewhere to ground. I replaced the blown transistor in the idle control unit and now it starts and idles even better than before.

[AirCooledCurtis]

Update. Today I replaced the whole O2 reference ground wire from pin 19 to the cylinder head. No change, still the same problem. I then started to look at the timing, since I haven't touched the distributor yet and everything else I've touched on this van revealed horrific repairs that the mind cannot comprehend. Well I started fiddling with the timing, a little advanced, a little retarded, and no change. More advance did wake it up off idle but it would backfire. It backfired and then started running on what seemed like 3 cylinders and I smelled raw fuel so I shut it off. I pulled the distributor and yada yada, the drive gear on the distributor was 180° off, and the distributor had been jammed into the hole, not even fully seated or engaged, 180° off from the gear (so that #1 is where you'd expect it). I clocked the drive gear on the distributor correctly, then installed the distributor, and it just won't idle. When I get it to run long enough to run around to the back to put the timing light on it, I can have a steady 5° of timing on it, but when it chokes out, the timing goes way crazy and retarded. I cannot seem to find anything else wrong. The wacky timing makes me think that it's the hall sensor. This distributor is not original. I'll also have to smoke the intake I think, it doesn't run any different with the brake booster or vent from the breather tower capped. It's backfired many times before.

[do.dah]

Not original dizzy? After mrkt?
There are vendors, our main vendors, that sell a replacement dizzy, that I THINK is a reproduction of a Passat, or Jetta? I don't totally remember. But the cap/rotor is different, and you can't take a vanagon cap/rotor and fit it properly to the dizzy. Iirc, the after mrkt dizzy also lands the #1 plug terminal location in a different place.

If it's after mrkt, it probably won't have very fine wires visable inside and at the bottom of the dizzy for the hall sensor.

Try looking up the GW/VC, burley, maybe vanagain, bus depot replacement dizzy's, some of them, maybe all of them, will say something about the differences, and how to address an install.

I also seem to recall that the after mrkt dizzys have been discussed here on the samba.

[AirCooledCurtis]

It's an aftermarket one. I've got an original coming from a friend. I'm thinking that where the engine thought TDC was (for each cylinder) and where the rotor and cap line up are not correct, judging by it would retard timing as much as what seemed like 20°ATDC (not possible on the Digifant map) when the engine began to stall the few times I got it to run long enough to put a timing light on it to confirm 5°BTDC at idle.

[AirCooledCurtis]

I took a break from this. I installed an original distributor, there's a place to plug a ground, though it's grounded to the engine. It has a new ground strap from the ground by the coil to the head, new pin 19 wire from ecu to the head. Once it gets some temp into it it won't want to transition off idle or make any kind of power enough to move the van forward under 2k rpms. Above 2k it's fine. If I get caught when the light turns green a key cycle will fix the issue for long enough to get out of the way. The only component I haven't replaced is the AFM, and the entire harness. O2, ECU, distributor, fuel pump, injectors cleaned and flow tested. I also haven't replaced the distributor cap. Also after installing the distributor correctly after it had been jammed in backwards, was when the issue got better enough that it could be driven.

[AirCooledCurtis]

Okay, I took a moment to collect my thoughts.

I unplugged the O2 signal wire just now, and put a couple of miles on it. It's not as peppy as before, but no poor running, no dead spots, no hesitancy etc. This rules out the AFM in my books, that's the only mixture/load related sensor the ECU is seeing, and there's no dead spots anywhere in the rev range.

This O2 issue is the same that I had experienced with my other '86 2WD. It'd run okay for a few minutes, then progressively run worse until you key cycled it and that would get you a few seconds to a minute. An O2 sensor fixed that van.

This is O2 sensor number 3 that I've tried, granted the first was almost certainly bad, and the second was a 3 wire Bosch from my Volvo that I spliced in. The one in there now is a Bosch from Bus Depot. I've gotten plenty of Bosch parts that were bad right out of the box in the last 10 years.

[crazyvwvanman]

[AirCooledCurtis]

[AirCooledCurtis]

Long time no update, the transaxle was out getting rebuilt. During that time I mailed the AFM to a friend to have him test it on his van, it didn't run well but had different issues than my motor was having. He mailed me back a recently rebuilt Fuel Injection Corp AFM that came off of a WBX that got the parts cannon before the owner gave up and did a swap.

So now to today. The replacement AFM runs better. It no longer gets into the funk where once the engine is warm throttle inputs will stall the engine needing a key cycle. Off idle and under 2k rpm hesitation under load is still present. At any engine temp give the throttle a stab and it will stumble and not rev. Slowly lean into the throttle and it behaves okay, this happening in both open and closed loop. Mixture under 2k rpms feels lean, it should feel quicker. It idles perfectly.

I replaced the coil since I had a suspicion that heavy loads down low where blowing out a weak spark when cylinder pressure is highest. This didn't make a difference. Now that it's running well enough, I timed it to 35° max timing following the GoWesty procedure and that may have improved it a tad. Currently it's driveable just fine but it's still dead with higher loads down low, mostly when cold now, it seems to work better when in closed loop unlike before the AFM change.

Things that I've tested or replaced/fixed having been ruled faulty

Distributor (now good used original) plug wires, BP6ET plugs, Fuel Injection Corp AFM, Bosch O2, signal wire for O2, idle control unit, ECU, ground strap from head to chassis, ground wire for O2, adjusted and tested TPS, adjusted valves, tested for vacuum leaks (small leak from throttle plate shaft, not unusual and I've had other vans that were the same), ignition coil, Set timing to 35° max, The brake booster vacuum check valve works as it should, Injectors cleaned and flow tested, fuel pump, fuel pressure tested while engine off, no exhaust leaks. I vaguely remember testing the ECT at the ECU plug. All of these parts were not parts cannoned. They were actually faulty minus the ignition coil and ECU.

Is it possible that the fuel pressure regulator is slow to respond? Like maybe a quick blip doesn't increase fuel pressure a few PSI as manifold vacuum drops? I suppose I could just cap the vacuum port and see if a constant elevated fuel pressure solves this.

I haven't touched the AFM mixture screw yet, I'm going to leave the flapper door mechanism alone since I know it's been recently set up.

[1988M5]

Just for fun, throw a set of new spark plugs in it with the correct gap. I had a BMW kick my but once from new plugs with too small of a gap. You don't adjust or check the gap with regular feeler gauges, instead use the coin/ramp type:

https://www.walmart.com/ip/Spark-plug-gap-gauge-to...239efccc50

BK
_________________
1991 tin top GL
2002 Winnebago Vista. VW VR6 24V Eurovan front clip powered class C 21' RV.
Some BMWs.

[AirCooledCurtis]